1. Field of the Invention
The present invention relates to an auto balancing apparatus for a disk drive, and in particualr to an auto balancing apparatus for a disk drive which is capable of automatically balancing an up and down movement of a disk when a disk mounted on a turntable is rotated.
2. Description of the Background Art
As a disk drive is designed to rotate at a high speed, a disk rotation unbalance problem(an up and down movement of a disk) occurs when a disk is rotated at a high speed.
In the conventional art, it is impossible to implement an accurate signal recording and reproducing operation due to the above-described disk unbalance rotation problems.
The above-described disk unbalance rotation generally occurs due to a non-uniformly fabricated disk. As the disk is designed to rotate at a high speed, the disk unbalance problem is considered as an important problem.
In the case that a disk is not accurately mounted on a turntable and is rotated, the above-described disk unbalance problem may occur.
In order to overcome the above-described disk unbalance rotation problem which generally occurs when the disk is rotated at a high speed, an auto balancing apparatus is introduced by the conventional art. The construction of the auto balancing apparatus will be explained.
As shown in FIG. 1, a rotary shaft 6 is rotatably installed on an upper surface of a substrate 1 in a vertical direction.
A turntable 7 is tightly inserted onto an upper portion of the rotary shaft 6, and a circular member having a certain thickness is formed on a lower surface of the turntable 7, and a ball casing 9 having a space 9a for receiving a plurality of balls 10 therein which are made of a metallic material, is formed in the circular member.
The center portion of the ball casing 9 is tightly inserted onto the rotary shaft 6.
A racing face 9i is formed on an inner wall in the space 8a  9a formed in the ball casing 9. The balls 10 roll on the racing face 9i based on a centrifugal force in order to correct a  an unbalance rotation which occurs when a disk is rotated at a high speed.
A magnet 11 is engaged at a portion neighboring with the rotary shaft 6 in the inner space 8a  9a of the ball casing 9, buffering portion(not shown) made of a rubber is formed on an outer surface of the magnet 11.
When the apparatus is not driven, the magnet 11 prevents the balls from being freely moved in the space.
A spindle motor 3 is installed below the ball casing 9. A rotor 5 which is one element forming the spindle motor 3 is integrally engaged to the rotary shaft 6. A stator 4 which is one element forming the spindle motor 3 is installed on an upper surface of the substrate and is fixed on an outer surface of a bearing 2 inserted onto the rotary shaft 6.
In the drawings, reference numeral 5M represents a magnet of the rotor 5, 8 represents a clamp for fixing the disk, and 16 represents a rubber which contacts with a lower surface of the disk and supports the disk.
The operation of the conventional auto balancing unit will be explained.
First, as the spindle motor 3 is driven, the rotor 5 is rotated, and the rotary shaft 6 is rotated. As the rotary shaft 6 is rotated, the turntable 2 is rotated, so that the disk mounted on the upper surface of the turntable 2 is rotated.
At this time, when the disk is rotated at a high speed, and an unbalance rotation problem occurs at the disk, the balls 10 inserted in the ball casing 9 are moved along the racing face 9i of the ball casing 9 and the unbalance rotation of the disk is corrected.
Namely, when the rotation of the disk exceeds a certain speed and an unbalance disk rotation problem occurs, the balls 10 are moved to a portion in which a certain resonance occurs. As a result, the unbalance rotation of the disk is corrected.
The above-described conventional auto balancing apparatus has the following problems.
First, the balls move freely in the interior of the ball casing in the radial direction, and the rotation cycle of the turntable and the rotation cycle of the balls are different. As a result, a self-excited vibration occurs, which makes it is impossible to implement a balancing operation.
In addition, magnets are serially installed on the portions around the rotary shaft. When the apparatus is not driven, the balls are pulled in one direction and then, are attached to the magnets. The attachment of the balls to the magnets results in an improper balancing operation.
When using the disk drive in a vertical direction, the balls are not rotated based on the centrifugal force. As a result, the balls do not properly race on the racing face of the ball casing, and it is impossible to implement a balancing operation.
The spindle motor, the ball casing and the turntable are sequentially installed below the rotary shaft installed on the upper surface of the substrate in the vertical direction. Thus, large space for installing the above-described elements is required, and the entire height of the disk drive apparatus is increased.
Namely, since the ball casing for implementing an auto balancing operation is positioned between the turntable and the spindle motor, the length of the rotary shaft is increased, and the entire height of the disk drive is increased.
Furthermore, when separately forming the spindle motor, the ball casing and the turntable, the total weight of the elements which are rotated by the spindle motor is increased, and the power consumption for driving the spindle motor is increased.